One important function required in an RFID system is to rapidly and efficiently identify tags. However, in a case where a plurality of tags exist within an identification range of an RFID reader, since all the tags attempt to respond through an equal channel at the same time, collisions occur, thereby delaying tag identification. Also, an idle phenomenon where tags do not respond at all may occur in a certain channel, which also decreases the efficiency of tag identification. Therefore, it is necessary to develop an RFID tag identification method capable of maximizing the efficiency of an RFID system by controlling inevitable collisions, the idle phenomenon, and the like, to be minimized under the limited functions of tags.
With rapid development of information communication technologies, efforts are being made to create a ubiquitous environment in which information communication devices can be easily and conveniently used in regular life, regardless of time and place. In order to create such a ubiquitous environment, a wireless identification technology enabling information communication devices to efficiently perceive and identify each other from a remote is necessary. The RFID technology is becoming attractive as a representative wireless identification technology.
The RFID is one of automatic identification technologies, such as a barcode, a magnetic sensor, an IC card, and the like, and is the most up-to-date technology used for wirelessly identifying data stored in a microchip by using an ultra-short wave or a long wave. The RFID technology is increasingly used in the industrial world to such a degree that the RFID technology is regarded as a substitute technology for the barcode, which is currently used in distribution and circulation fields, financial services, etc.
FIG. 1 is a block diagram illustrating the configuration of a conventional RFID system.
As shown in FIG. 1, in order to identify a tag 120 attached on an object, a conventional RFID reader 110 identifies an identifier stored in the tag 120 by transmitting/receiving RF signals to/from the tag 120.
In this case, tag identification protocols used for the conventional RFID reader 120 to identify the tag 120 may be roughly classified into Aloha-based protocols and tree-based protocols.
The Aloha-based protocols include a pure Aloha protocol which cannot control collisions between identifiers, the idle phenomenon, and the like at all, a slotted Aloha protocol which can control collisions and occurrence of the idle phenomenon through time slots, and a frame-slotted Aloha protocol which can more efficiently control collisions and the occurrence of the idle phenomenon by grouping slots in units of frames. Here, the collision phenomenon between identifiers represents that the conventional RFID 110 receives two or more identifiers at the same time, and the idle phenomenon represents that the conventional RFID 110 cannot receive an identifier during a certain time period.
Meanwhile, the tree-based protocols employ a method of dividing tags into two groups upon occurrence of a collision and extending the search space.
Of the Aloha-based protocols and the tree-based protocols, the Aloha-based protocols are expected to be used as a standard for the RFID technology.
As described above, the Aloha-based protocol, and especially the frame-slotted Aloha protocol, which is to be widely used in the future, employs a method in which each of one or more tags selects one slot within a frame size, which corresponds to the number of slots constituting one frame, the efficiency of tag identification significantly varies depending on the adjusted frame size. For example, in an environment where a plurality of tags 120 exists around the RFID reader 210, if the RFID reader 210 uses too small a frame size, the number of collision slots increases, so that the tag identification performance becomes degraded. In contrast, if the RFID reader 210 uses too large a frame size, the number of idle slots increases, so that the tag identification performance becomes degraded.